Gasification of carbonaceous solids



July 13, 1954 P. W. GARBO GASIFICATION 0F CARBONACEOUS SOLIDS Fiied May29, 1948 50L /.D P5571705 IN V EN TOR.

PULWGAO A TTORNE Y5 Patented July 13, 1954 UNITED OFFICE GASIFICATION OFCARBONACEOUS SOLIDS Application May 29, 1948, Serial N 0. 30,023

3 Claims.

This invention relates to a method and apparatus for gasification of asolid carbonaceous material. In one of its more specific aspects, thisinvention relates to a process of gasification of a solid carbonaceousmaterial containing volatile constituents wherein distillation ofvolatile constituents and reaction of the residual solid with a gaseousreactant are carried out.

Solid carbonaceous materials which may be treated by the present processinclude coal, coke, oil shale, lignite, and the like. The invention isparticularly applicable to treatment of coal and similar carbonaceousmaterials comprising volatile constituents wherein both carbonizationand chemical reaction are employed to gasify substantially all of thenon-mineral content of the carbonaceous material. The process of thisinvention is also useful for carbonization of coal, or partialgasification, as well as for complete gasification.

Of the chemical reactions employed in gasifification, reactions in whichcarbon is chemically combined with oxygen or hydrogen are most commonlyused and best adapted to the process of this invention. Illustrativegasifying reactants include oxygen, steam, carbon dioxide, hydrogen ormixtures of these gases.

Many and diverse methods have been practiced and proposed for thegasification of solid carbonaceous materials. technique has been appliedmore or less successfully to processes for the gasification of variouscarbonaceous materials. For example, coal in finely-divided form may betreated in a fluidized bed with hot inert gases to effect removal ofvolatile constituents or with a gas containing reactive oxygen to effectgasification by chemical reaction to any desired extent. Fluid bedgasification is particularly adapted to the treatment of coke or hardcoal, such as anthracite, which have little or no tendency toagglomerate under reaction conditions. Coking coal may be treated priorto gasification to prevent agglomeration. Such pretreatment may consistof heating the coal to drive off a portion of the volatile constituentstherefrom or partial preoxidation of the coal with an oxygen-containinggas, nitric acid or other oxidizing agent. Agglomeration may be avoidedor minimized by admixing the raw coal with sufficient carbon, char, ashor inert refractory material in finely-divided form to substantiallyprevent agglomeration of the raw coal particles.

The gasification of coal and the like to produce a mixture comprisingcarbon monoxide and hy- The fluidized solid drogen is often desirable.It is known that carbon monoxide and hydrogen may be converted tovarious hydrocarbons. The conversion of carbon monoxide and hydrogen tohydrocarbons suitable for use as motor fuels is satisfactorily carriedout under elevated temperatures and pressures in the presence of acatalyst, generally one comprising an element of the iron group of theperiodic table of the elements.

At the present time the synthesis of hydrocarbons from carbon monoxideand hydrogen is of considerable importance commercially. The conversionof solid carbonaceous materials to high B. t. u. value heating .gas isalso of increasing importance. For these reasons, it is most desirableto develop a simple and economical process for the conversion of solidcarbonaceous materials to gaseous reactants suitable as feed stock forthe hydrocarbon synthesis or to gaseous mixtures of high B. t. u. valuefor fuel purposes.

A problem in the gasification of carbonaceous materials which has notbeen solved entirely satisiactorily is that of economically convertingfresh coal to gaseous products of value as fuel gas or snythesis gas.

An object of the present invention is to provide an improved process forthe gasification of solid carbonaceous material.

Still another object is to provide an improved process for combinedcarbonization and gasification of solid carbonaceous materialscontaining volatile constituents.

A further object of the present invention is to provide such a processwhich is particularly applicable for use in gasification of coal, oilshale, lignite, and the like.

The present invention provides a simple improved method for thegasification of solid carbonaceous materials to produce either a gaseousproduct suitable as feed for the synthesis of hydrocarbons andoxygenated derivatives or a heating gasof relatively high B. t. u.value. The process may be operated to produce a high grade char as asolid residue or may be operated for substantially complete gasificationof the feed material, leaving only ash as the residual solid.

In accordance with this invention, the solid carbonaceous material of aparticle size suitable for fluidization, generally less than about 0.1inch in diameter, is charged to the top of a fluidized bed of saidparticles in a gasifier. The gasifier is characterized by the unusualfeature that despite good fluidization of the particles there are zonesin which top-to-bottom mixing of solid particles is inhibited. This isaccomplished by providing zones of the gasifier with a number ofpartitions disposed vertically in the bed of fluidized solid particles.Thus the advantages of fiuidization may be retained while at the sametime obtaining advantages peculiar to a non-fluidized moving bed,articularly, countercurrent flow of gases and solids and a temperaturegradient along the vertical dimension of the gasifying vessel. Theparticles of carbonaceous material flow downwardly through the gasifiercountercurrent to a stream of fluidizing gas. The fluidizing gas isintroduced in the lower portion of the bed of solid particles and maycomprise a reactant gas, preferably free oxygen. The efiiuent gas orproduct gas is withdrawn from a point above the fluidized bed andcomprises any products of distillation, as well as the gases resultingfrom chemical reaction.

As the carbonaceous material flows downwardly through the gasifier, itpasses progressively through a solid preheating zone, which may be adistillation or carbonizing zone; a reaction zone; and, preferably, alsoa gas preheating zone which may also be a carbon cleanup zone. Thesezones preferably are all included within a single vessel. In theuppermost or solid preheating zone, the coal is brought into contactwith hot gaseous products from the reaction zone. Heat from the gaseousproducts is transferred to the particles, preheating them and drivin offany volatile constituents contained therein. This solid preheating zoneis designed to prevent or greatly minimize top-to-bottom mixing of thesolids moving downwardly therethrough. A temperature gradient is thusestablished along the height of this zone with the lowest temperature atthe top of the zone and the highest at the bottom. In the reaction zone,the carbonaceous material is reacted with the gasifying reactant in thefluidizing gas stream, for example, oxygen, liberating heat andgenerating gaseous products comprisin carbon oxides. In the reactionzone, the solids are free to move with the complete turbulencecharacteristic of fluidization so that a substantially uniformtemperature exists throughout the I The residual solid material,

reaction zone. which may be low carbon char or ash, may be withdrawndirectly from the reaction zone but preferably is withdrawn after it hasbeen made to pass downwardly through a gas preheating zone wherein ittransfers heat to the incoming gaseous stream. A reactant gas may bepassed upwardly through this zone to improve carbon cleanup.

Where a gas preheating zone is employed, it is like the solid preheatingzone in that the fluidized solids flow downwardly through elongatechannels of restricted horizontal cross-section which curtailtop-to-bottom mixing of the solids. Under these circumstances, theincoming gases flow countercurrently to the solids, establishing atemperature gradient along the vertical dimension of the channels withthe highest temperature at the top thereof and the lowest at the bottom.Where the incoming gases are reactive with the carbon residue leavingthe reaction zone, a desirable composition gradient is also establishedin the channel of the gas preheating zone, that is, the residue has thehighest carbon content at the top of the channels and the lowest at thebottom.

This process effects an economical gasification of coal and other solidcarbonaceous materials particularly those containing volatileconstituents. Since the heat from the solid residue is transferred tothe incoming gas stream and the eflluent 4 gases give up heat to theincoming fresh solid feed material, a highly efficient system isprovided which utilizes heat in a most economical manner.

The present invention will be described in detail with reference to coalas the carbonaceous material to illustrate the operation of the processof this invention. It will be understood that coal is used as a specificexample and that the method of the invention as described is not limitedto the use of coal as the feed material. Since the gasification ofvarious materials is known in the art, the application of the presentinvention to other solid carbonaceous materials will be evident to oneskilled in the art from the detailed description of this invention andthe illustrative example of its application to treatment of coal.

Fig. 1 of the accompanying drawing is a diagrammatic elevational view incross-section of apparatus suitable for carrying out the process of thepresent invention.

Fig. 2 is a horizontal section through the apparatus illustrated in Fig.1 taken along the horizontal plane 2-2.

With reference to the drawing, the coal is fed into a vessel l0 througha line H at a rate regulated by a control valve [2, suitably a rotary orslide valve for handling solids. The vessel [0 suitably is a pressurevessel, generally similar in construction to conventional reactorswherein a fluidized bed of catalyst or carbonaceous material isutilized. Thus the vesesl is provided with a conical bottom [3 fordistribution of the fluidizing gas, and with an enlarged upper section Mfor separation of solids from the effluent gas above the fluidized bed.The gasifier is, in general, somewhat more elongated than theconventional fluidized bed reactor so that the bed is relatively deeperthan the typical fluidized bed, the purpose of which will be brought outmore fully hereinafter.

Gas for fluidization and reaction is introduced to the vessel throughline !6 and distributed by a suitable perforated distribution ring I 1.Residual solid material from the bottom of the vessel is withdrawnthrough line l8 at a rate controlled by the control mechanism [8 whichmay suitably be a screw-type conveyor or a rotary valve. Effluent gasesare withdrawn from the vessel at a point above the upper level of thefluidized bed through line 2|. A suitable filter 22 may be provided atthe gas outlet to effect removal of fines from the efliuent gas stream.

The gasifier is divided essentially into three zones, namely, a solidpreheat zone 23, a reaction zone 24 and a gas preheat zone 25. Zones 23and 25 are provided with a plurality of spaced partitions 26 which aredisposed longitudinally within the reactor to divide these zones into amultiplicity of longitudinally extending passages or channels 21disposed axially along the reactor. These passages 21 substantiallyprevent top-tobottom mixing of the solid material in the solid and gaspreheat zones of the reactor. The partitions 26 may take various formsto provide longitudinally extending cells or passages of any desiredcross-sectional configuration. Fig. 2 illustrates only one example of anarrangement of partitions which is suitable for the purpose. Numerousother arrangements will occur to those skilled in the art which will befunctionally equivalent to the arrangement illustrated.

The passages should be so dimensioned that they have an effective sizeof a pipe having an internal radius falling within the range from aboutinch to about 2 inches, preferably from inch to about 1 inch. Thus if apassage has an eflective pipe size corresponding to an internal radiusof, for example, inch, no solid particle flowing therethrough will bespaced from a wall by distance greater than inch, and the distancebetween a particle and the wall farthest away will be not greater than 1inch. With the partitions spaced within the range above indicated, andpassing a gaseous medium therethrough at a suitable velocity, readilydetermined by trial, depending on the density and particle size of thesolid material, top-to-bottom mixing of the solid particles in thepassages is prevented to an extent sufiicient to maintain a temperaturegradient therethrough.

It is advantageous in the practice of this invention that the solidcarbonaceous material be in the form of a powder, substantially all ofwhich passes a 40 mesh secreen. The most advantageous particle size forany given system will depend upon the density of the material, the shapeof the particles, the density and velocity of the fiuidizing gas, thesize of the passageways, etc.; the optimum particle size for any givensystem is readily determinable by simple preliminary experimentsconducted under conditions simulating those of actual operation.

The carbonaceous material treated is maintained in the reactor in astate of dense phase fiuidization. Under these conditions the particlesare agitated by the gas stream and individually exhibit random movement.The upper surface of the bed or mass assumes a level, substantiallyabove the normal level of the settled particles, which level is commonlyknown as a pseudo-liquid level. Under fluidized conditions the uppersurface of the bed is disrupted by movement of the gas therethrough andresembles in appearance the surface of a boiling liquid.

In the conventional fluidized bed, there is thorough top-to-bottommixing of the particles in the bed so the entire bed becomes ahomogeneous mixture having a uniform temperature throughout. In thepresent invention, on the other hand, top-to-bottom mixing is preventedin the heat transfer zones of the gasifier.

During the flow of the gaseous medium through the bed or mass ofparticles in the gasifier, the

individual particles rise and fall but the general direction of movementof the particles is downward through the gasifier. Thus as the operationof the process progresses, fresh incoming particles form the uppersurface of the mass and gradually progress downwardly toward the bottomof the bed. As the particles progress downwardly they are subjected topreheating, chemical reaction, and heat transfer to the incomingfluidizing gas. The residual solid material is removed from the lowerportion of the gasifier.

The solids withdrawn from the lower portion of the gasifier may comprisechar of any desired carbon content or ash substantially free fromcarbon. In general, the residual solid obtained from treatment of coal,lignite and the like, is a char of low carbon content.

The operation may be carried out so as to accomplish distillation ofvolatile constituents from the feed material, e. g., coking of coal,with only sufiicient oxidation to supply heat required for thedistillation. In such an operation, with coal as feed, a high qualitychar may be obtained as the residual solid. This char may find use as ahigh grade smokeless fuel or it may be used wherever a high carbon charis indicated.

In some instances it is economically desirable to produce low grade charof limited fuel value. In such an instance the char may serve, underfavorable conditions, as fuel for power generation or the like,particularly where the char may be used as fuel in the locality of thegasifier. In other circumstances, it is desirable to convertsubstantially all of the carbon content of the feed material to gases.Under these circumstances, substantially carbon-free ash is desired asthe residual solid. The desired degree of conversion is readilycontrolled by the process of my invention by control of the rate of flowof solids and gases through the gasifier.

An outstanding characteristic of the gasifier described above is theability to achieve countercurrent flow of the gases and fluidized solidsand maintain a temperature gradient in the gas and solid preheatingzones. Thus, in the solid preheating zone, the fluidized solid movesdownwardly through the channels generally countercurrent to theupflowing gas stream. The partitions substantially eliminatetop-to-bottom mixing of the particles. Thus, contrary to the situationexisting in a conventional fluidized bed, the particles of solid in thesolid preheating zone are at a considerably higher temperature at thebottom of the preheating zone than at the top. The extent of preheatingmay be determined by design, the highest temperature being close to thereaction temperature. Similarly, the solids are progressively cooled asthey pass downwardly through the gas preheating zone below the reactionzone. The gas is progressively heated as it flows upward through the gaspreheating zone. In the zone where chemical reaction takes place it ispreferable to permit conventional fluidization with top-to-bottom mixingand a uniform temperature therethroughout.

The use of powdered fuel in a state of dense phase fluidization providesexceptionally high surface area of the solid fuel per unit of volume inthe heat exchange zones and exceedingly intimate contact between the gasand the solid particles. The agitation of the solid particles promoteshigh rates of heat transfer. This insures optimum conservation of heatand most efficient transfer of heat between the solid particles and thegas streams.

It is contemplated that in some instances means will be provided forsupplying heat from an external source to the fluidized reaction zone ofthe gasifier. For example, fire-tubes or elec tric arcs or electricresistance heaters may be disposed in reaction zone 24 of the gasifierl0 shown in the drawing.

It is noteworthy that the process of the invention is applicable tocoking coals which may be fed to the gasifier without any pretreatmentto alter their coking properties. Since the coal particles charged tothe gasifier of this invention pass through a preheat zone in which thetemperature of the particles is gradually increased and the particlesflow countercurrently to gases ascending from the reaction zone, it ispossible to alter at least the surfaces of the coal particles so thatthey exhibit little or no agglomerating tendency during processing bythis invention.

Obviously, many modifications and variations of the invention as aboveset forth may be made without departing from the spirit and scopethereof, and therefore only such limitations should be imposed as areindicated in the appended claims.

*aeeacm I claim:

1. In a process for the gasification of a solid carbonaceous material,the improvement which comprises passing a mass of solid carbonaceous.top of said zone to the bottom thereof and having a relatively small,uniform cross-sectional area; passing hot gaseous products of reactionupwardly through said zone at a velocity which maintains the particlesin said streams in a state of dense phase fiuidi'zation therebymaintaining an ascending temperature gradient in said streams ofparticles and a descending temperature gradient in said gaseous productsof reaction; discharging the resulting preheated streams of particlesdirectly into the top of a common bed of said particles in an unimpededreaction zone; passing a preheated gaseous reactant upwardly throughsaid bed of particles in said reaction zone at an elevated temperatureeffecting partial gasification of said particles and forming said hotgaseous products of reaction and a particulate residual solid;withdrawing said residual solid from the bottom of said reaction zoneand passing said residual solid downwardly through a second heatexchange zone as a plurality of immediately adjacent separately confinedparallel streams, each of said streams ex tending from the top of saidsecond heat exchange zone to the bottom thereof and having a relativelysmall, uniform cross-sectional area; passing said gaseous reactant at a,temperature below said reaction temperature upwardly through said secondheat exchange zone at a velocity which maintains said residual solid ina state of dense phase fluidization thereby maintaining a descendingtemperature gradient in said streams of residual solid and an ascendingtemperature gradient in said gaseous reactant; passing the resultingheated gaseous reactant to said reaction zone as said preheated gaseousreactant and withdrawing the resulting cooled streams of residual solidfrom said'second heat exchange zone.

2. A process as defined in claim 1 wherein the gaseous reactant passingupwardly in said second heat exchange zone comprises a mixture of steamand oxygen.

3. A process as defined in claim 1 wherein said solid carbonaceousmaterial is coal.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,898,967 Schneider et al. Feb. 21, 1933 2,359,310 HemmingerOct. 3, 1944 2,394,814 Snuggs Feb. 12, 1946 2,436,225 Ogorzaly et alFeb. 17, 1948 2,444,990 Hemminger July 13, 1948 2,451,804 Campbell et alOct, 19, 1948 2,509,745 Riggs May 30, 1950 2,541,186 Anderson Feb. 13,1951 2,595,365 Odell May 6, 1952 FOREIGN PATENTS Number Country Date394,747 Great Britain July 6, 1933 586,391 Great Britain Mar. 18, 1947

1. IN A PROCESS FOR THE GASIFICATION OF A SOLID CARBONACEOUS MATERIAL,THE IMPROVEMENT WHICH COMPRISES PASSING A MASS OF SOLID CARBONACEOUSMATERIAL IN PARTICULATE FORM DOWNWARDLY THROUGH A HEAT EXCHANGE ZONE ASA PLURALITY OF IMMEDIATELY ADJACENT SEPARATELY CONFINED PARALLELSTREAMS, EACH OF SAID STREAMS EXTENDING FROM THE TOP OF SAID ZONE TO THEBOTTOM THEREOF AND HAVING A RELATIVELY SMALL, UNIFORM CROSS-SECTIONALAREA; PASSING HOT GASEOUS PRODUCTS OF REACTION UPWARDLY THROUGH SAIDZONE AT A VELOCITY WHICH MAINTAINS THE PARTICLES IN SAID STREAMS IN ASTATE OF DENSE PHASE FLUIDIZATION THEREBY MAINTAINING AN ASCENDIGNTEMPERATURE GRADIENT IN SAID STREAMS OF PARTICLES AND A DESCENDINGTEMPERATURE GRADIENT IN SAID GASEOUS PRODUCTS OF REACTION; DISCHARGINGTHE RESULTING PREHEATED STREAMS OF PARTICLES DIRECTLY INTO THE TOP OF ACOMMON BED OF SAID PARTICLES IN AN UNIMPEDED REACTION ZONE; PASSING APREHEATED GASEOUS REACTANT UPWARDLY THROUGH SAID BED OF PARTICLES INSAID REACTION ZONE AT AN ELEVATED TEMPERATURE EFFECTING PARTIALGASIFICATION OF SAID PARTICLES AND FORMING SAID HOT GASEOUS PRODUCTS OFREACTION AND A PARTICULATE RESIDUAL SOLID; WITHDRAWING SAID RESIDUALSOLID FROM THE BOTTOM OF SAID REACTION ZONE AND PASSING SAID RESIDUALSOLID DOWNWARDLY THROUGH A SECOND HEAT EXCHANGE ZONE AS A PLURALITY OFIMMEDIATELY ADJACENT SEPARATELY CONFINED PARALLEL STREAMS, EACH OF SAIDSTREAMS EXTENDING FROM THE TOP OF SAID SECOND HEAT EXCHANGE ZONE TO THEBOTTOM THEREOF AND HAVING A RELATIVELY SMALL, UNIFORM CROSS-SECTIONALAREA; PASSING SAID GASEOUS REACTANT AT A TEMPERATURE BELOW SAID REACTIONTEMPERATURE UPWARDLY THROUGH SAID SECOND HEAT EXCHANGE ZONE AT AVELOCITY WHICH MAINTAINS SAID RESIDUAL SOLID IN A STATE OF DENSE PHASEFLUIDIZATION THEREBY MAINTAINING A DESCENDING TEMPERATURE GRADIENT INSAID STREAMS OF RESIDUAL SOLID AND AN ASCENDING TEMPERATURE GRADIENT INSAID GASEOUS REACTANT; PASSING THE RESULTING HEATED GASEOUS REACTANT TOSAID REACTION ZONE AS SAID PREHEATED GASEOUS REACTANT AND WITHDRAWINGTHE RESULTING COOLED STREAMS OF RESIDUAL SOLID FROM SAID SECOND HEATEXCHANGE ZONE.